According to death dates on their markers (findagrave.com), Lucretia Ray died on Jan. 11, and Elizabeth Amy Ray died on Jan. 15.
This is from a NY paper, slightly different story:
POISONED UNCLE AND AUNTS. Nephew Kills His Relatives to ______ Property—Suicide After Arreet. Fort Worth, Texas. — Robert Ray poisoned a family of three persons on a ranch fifty miles south of Pecos a few days ago. The dead are T. J. Ray and his two sisters, Louise and Amy, the latter being seventy years of age. The poisoner was a nephew of Ray and was heir to the ranch property, which fact is thought to have prompted the commission of the crime. Soon after the death of the three people young Ray loaded his wife and child into a wagon and drove to Pecos and boarded a west-bound train for Colorado City. Arriving there he was arrested by the Sheriff. When Ray saw the officer he swallowed a dose of poison and died soon after. The Rays resided on a little ranch about fifty miles southeast of the town of Pecos. The poison was administer- ed to the three people in their food.
Poor Elizabeth Amy if she lingered for 4 days!
You might check with the Mitchell County library to see if there are newspapers from that time period.